If the place is completely booked for the selected time, you should be able to add your name to a waiting list. Then you'll get a notification, and you'll be first in line for the slot if it opens up. All people on the waiting list will get a notification. All of them will be able to indicate if they want the slot. After a certain amount of time, if at least one person on the waiting list has indicated that they want the slot, then the person who was closest to the front of the line will get it. Everyone else will be notified that they didn't get it. Anybody who doesn't respond or who says they don't want the slot anymore will be removed from the waiting list, and the slot will be marked as having an opening.
If the place is completely booked for the selected time, you should be able to add your name to a waiting list. Then you'll get a notification, and you'll be first in line for the slot if it opens up. All people on the waiting list will get a notification. All of them will be able to indicate if they want the slot. After a certain amount of time, if at least one person on the waiting list has indicated that they want the slot, then the person who was closest to the front of the line will get it. Everyone else will be notified that they didn't get it. Anybody who doesn't respond or who says they don't want the slot anymore will be removed from the waiting list, and the slot will be marked as having an opening.